The present invention relates to methods and apparatus for producing an improved insulation and, more particularly, to a method and apparatus to impregnate cellulose fibers with a chemical solution to impart to the cellulose fiber fire and/or pest resistance.
Cellulose fiber thermal insulation generated from hammermilled newspaper has been used as a loose-fill insulation in buildings for more than thirty years. In order to reduce the fire hazard connected with this type material, various dry chemicals have been blended into the milled fibers, most notably, mixtures of powdered borax, such as sodium borate pentahydrate and boric acid. Fortuitously, these borates also give the finished material some measure of pest resistance. To obtain an acceptable flame spread resistance, this process requires a weight ratio of dry chemicals to cellulose fiber of about 1 to 3. Although various other dry chemicals have been utilized for imparting fire resistance, these chemicals usually require higher dose rates and introduce other problems, such as corrosiveness, toxicity, cost, microbial activity and adverse moisture absorption characteristics. A survey of the various chemicals and techniques utilized and representing the state of the art is given by R. W. Anderson of the U.S. Government's Energy Research and Development Administration in a paper entitled "Survey of Cellulose Insulation Materials," dated January 1977, and available through the National Technical Information Service (NTIS). A significant problem cited is the gross separation of the dense chemical particles from the fibers leaving the fibers unprotected, causing excessive dust and waste of chemical.
Until recently, the utilization of borates to chemically treat cellulose fiber materials to provide a thermal insulation has been adequate although wasteful. However, as the cost of domestic energy has burgeoned, the demand for all forms of thermal insulation has increased dramatically. With the advent of increased demand for cellulose fiber insulation, a proportionally increased demand for a supply of borate chemicals also appeared. However, the supply of borate chemicals was found to be somewhat inelastic and severe shortages of borates and, consequently, of properly treated cellulose fiber insulation came into existence accompanied by volatile prices and speculation with existing supplies. It has consequently become apparent that a substitute chemical, as well as a new process for manufacturing cellulose fiber insulation having permanently adequate fire retardant properties, is needed.
The textile industry has long known of the effectiveness of many chemical fire retardant agents which are utilized at much lower proportions to cellulose fiber content than has been practiced by the insulation industry utilizing borates. For example, one method of fireproofing textile fabrics has been to dip the material in a solution of specific concentration leaving a residual chemical intimate with and thoroughly absorbed in the fibers. Such dip and dry techniques are not practical in the cellulose fiber insulation industry because the cellulose fiber particles are very small, loose and not readily subject to such a dipping and drying process. Furthermore, it is not known which chemical agents offer the best combination of properties for both manufacturing and the finished product. Thus, even though the textile industry has fire-proofed textiles by the dipping and drying process, such a technique does not indicate how loose fiber may be impregnated with a wet chemical. Furthermore, the technical grade phosphates utilized in the textile industry are far too expensive for economic utilization in cellulose fiber insulation even at the lower residual treatment concentrations applied to the textiles.
It has been found that agricultural grade phosphates provide adequate fire-retardance, constitute a less expensive chemical than any of the various borates and may be utilized in substantially smaller ratios (see "Ammonium Polyphosphate Liquid Fertilizer As A Fire Retardant For Wood," American Wood-Preserver's Association, 1969, pages 1-12, by Eckner, Stinson and Jordan; and "Fire Suppression & Detection Systems," Glencoe Press 1974, by John L. Bryan.) However, such lower cost agricultural phosphates are difficult to pulverize and do not adapt to the dry blending process with reasonable yield or effectiveness. Furthermore, the more common of the agricultural phosphates (diammonium orthophosphate) has been found unstable in solution, in milling and at elevated temperatures, tending to evolve free ammonia which is an unacceptable nuisance in the manufacturing process. The use of agricultural grade phosphates in conventional wet blending processes can involve a high energy cost for a subsequent drying and is, therefore, impractial as well. The required tolerances within which variations in the proportion of the various constituents may vary cannot be practically achieved in continuous dry blending processes. Unacceptable variations in the proportions are further exacerbated by the fact that there is generally insufficient adhesion of the dry chemical to the fibers to prevent gross separation of the chemical and the cellulose fibers during bagging, shipping and application.
Utilizing the method and process of the invention disclosed herein, the full potential of cellulose fiber insulation may be realized. Not only can sufficient process control tolerances be achieved in practice, but a superior loose fill insulation, particularly applicable in the insulation of existing buildings, is obtained. Furthermore, the present invention generates a fire retardant cellulose fiber insulation which remains intact even in the presence of direct flame impingement and does not melt or contribute to fuel the fire. Because the present invention utilizes a wet impregnation and drying process, the fire retardant impregnation is complete and uniform assuring a uniformity of properties with no material separation. In addition, resistance to vermin and microorganisms is easily obtained by simply mixing into the solution traces of appropriate chemical or biocidal agents with the fire retardant chemical prior to impingement on the cellulose fibers. Corrosion protection can likewise be obtained with the addition of appropriate chemical inhibitors.
The raw materials, including the phosphates and the cellulose fibers, are low cost and widely available in large quantities. Furthermore, the cellulose fibers may be obtained from recycled newsprint and other waste materials which make optimal use, and thus conservation, of natural resources. In addition, the agricultural grade phosphates utilized in the present invention are among the most plentiful bulk chemicals available and, unlike borates, can amount to but a negligible fraction of the total use of such chemicals for agricultural purposes. Another advantage of the method and apparatus in accordance with the present invention is that the materials used are physically and chemically benign achieving the maximum of occupational safety and environmental protection in both the manufacturing and installation process. Furthermore, the finished product has a low content of very fine particles and, thus, a much reduced tendency to make dust. Finally, a principal advantage of the present invention is that the manufacturing plant involvement, know-how, energy and operating costs are less than for other types of insulation processes and the installation skills and equipment required are minimal and well known.